Rated 3 out of 5 stars

This is an excellent initiative. I am finding it difficult to adjust the font size in the message panel. Many emails I receive appear in very tiny font size (this is not the case when I disable the addon, somehow TB makes sure that all text comes in a consistent font size). When I use Ctrl+ to increase message font size it causes the interface's font size to increase. Conversely, when I use Ctrs+ when the addon is disabled, the interface's font size does not change. I don't know how to deal with this distortion. Probably someone can help?

This review is for a previous version of the add-on (2.7). 

The reason this happens is because of an underlying bug in Gecko, the rendering engine that powers both Thunderbird and Firefox. Long story short, until bug 80713 is fixed, I have no way to fix this easily. You can contact me in private if you're interested about the full technical details :-).